The photochemical properties of rhodopsin including quantum yields, bleaching intermediates and isomeric composition of the retinal products will be determined using excitation into the second and third transitions of the pigments. The effect of this higher radiation upon the structure of the opsin will be examined by Fourier transform infrared methods and pigment regenerations. A study of the bleaching intermediates of 9,13-isorhodopsin (isorhodopsin II) will be made in order to determine the relationship of the two-step photoisomerization process to visual excitation. The nature of the secondary interactions of the protein and the chromophore will be examined by characterizing the spectral properties of the chromophore in solution and the protein using Fourier transform infrared methods. Similar studies of isorhodopsin, 9,13-isorhodopsin and retinochrome will be made in order to observe common and/or particular shifts in the chromophore's spectrum. Retinal analogs containing an electronegative fluorine atom at various positions will be syntesized, various double bond isomers formed by UV radiation, isolated by high pressure liquid chromatography and analyzed by Carbon-13 nuclear magnetic resonance. They will be tested for pigment formation with bovine opsin and their properties studied by ultraviolet, circular dichroism and infrared spectroscopy. The electronic nature of the secondary protein-chromophore interactions can thus be examined, including any positional dependence.